Re: [PATCH v3 1/1] PCI/ERR: Fix reset logic in pcie_do_recovery() call

[Kuppuswamy, Sathyanarayanan]

On 9/28/20 4:17 AM, Sinan Kaya wrote:
> On 9/27/2020 10:43 PM, Kuppuswamy, Sathyanarayanan wrote:
> > FATAL + no-hotplug - In this case, link will still be reseted. But
> > currently driver state is not properly restored. So I attempted
> > to restore it using pci_reset_bus().
> >
> >           status = reset_link(dev);
> > -        if (status != PCI_ERS_RESULT_RECOVERED) {
> > +        if (status == PCI_ERS_RESULT_RECOVERED) {
> > +            status = PCI_ERS_RESULT_NEED_RESET;
> >
> > ...
> >
> >       if (status == PCI_ERS_RESULT_NEED_RESET) {
> >           /*
> > -         * TODO: Should call platform-specific
> > -         * functions to reset slot before calling
> > -         * drivers' slot_reset callbacks?
> > +         * TODO: Optimize the call to pci_reset_bus()
> > +         *
> > +         * There are two components to pci_reset_bus().
> > +         *
> > +         * 1. Do platform specific slot/bus reset.
> > +         * 2. Save/Restore all devices in the bus.
> > +         *
> > +         * For hotplug capable devices and fatal errors,
> > +         * device is already in reset state due to link
> > +         * reset. So repeating platform specific slot/bus
> > +         * reset via pci_reset_bus() call is redundant. So
> > +         * can optimize this logic and conditionally call
> > +         * pci_reset_bus().
> >            */
> > +        pci_reset_bus(dev);
>
> I think we have to go to remove/rescan for this case as you also
> mentioned above. There is no state to save. All BAR assignments
> are gone. Entire device programming is also lost.
>
> I don't think pci_reset_bus() can recover from this situation safely.
> It will make things worse by saving/restoring the hardware default
> state.
>
> This should remove/rescan logic should be inside DPC's slot_reset()
> function BTW. Not here.
Since there is no state restoration for FATAL errors, I am wondering whether
calls to ->error_detected(), ->mmio_enabled() and ->slot_reset() are
required?

Let me know your comments about following pseudo code.

if (fatal error & hotplug_supported)
   do nothing // if fatal triggered by DPC, clear DPC state.

if (fatal error & no-hotplug)
  perform slot_reset and renumerate affected devices.

>

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer